1. Field of the Invention
The present invention relates to sensing loads, and more specifically to sensing loads through use of an optical fiber positioned so that weight pressing on the fiber will cause attenuation in light passing through the fiber.
2. Description of the Related Art
There are many applications in which it is useful to be able to sense loads automatically, and in particular to sense the position and weight of the load. One particular area in which such capability is desirable is in determining the weight and position of a passenger in an automobile seat in order to determine the most appropriate deployment of an airbag in the event of an accident and, for example, to suppress such deployment in certain cases such as where the passenger is a small child. The requirement of next generation airbag suppression systems on all vehicles is being mandated for full implementation for all cars in the year 2008. This poses a technical challenge for which there are some proposed solutions. However, none of these solutions are simple enough to be readily manufactured and distributed.
The general task of ascertaining the weight and, to some extent the position, of a passenger in an automobile seat in connection with airbag deployment has been explored in the prior art. See, for example, Breed et al., U.S. Pat. No. 6,712,387. Breed describes a system and method for determining the presence of an occupant and/or the position of the occupant as well as various devices to control and influence the deployment of a side airbag. The system described in Breed includes a transducer arranged to receive waves from a space above a portion of a seat, and a signal representative of the presence and or position of the occupant is generated based upon the waves received by the transducer. In Breed, the determination of whether an occupant is leaning against the door or is possibly adjacent to the airbag module is important. “In these cases, deployment of the side airbag can be suppressed. In the alternative the time at which deployment of a side airbag starts, the rate of gas flow into the side airbag, the rate of the gas flow out of the side airbag and/or the rate of deployment of the side airbag is/are controlled.” Breed, Abstract.
However, Breed and other prior art systems have limitations that do not allow them to meet the new government regulations, which require more precise grading of passenger presence and weight class, in an economical system. For example, the computation of the relevant forces to determine the presence, size and location of a passenger in Breed requires use of a complex algorithm dealing with a neural net. Such methods are complex and require sophisticated analytic techniques and devices.
Optical fibers have been used for many years for communication through transmission of light. The characteristics of optical fiber are well known, and fiber has been assembled in any number of configurations. Those skilled in the art have come to understand that in communication applications the fiber should generally remain relatively straight, preferably subject to turns no tighter than a certain defined radius so that the transmission of light is attenuated as little as possible. The discussion of choice of fibers and conditions for maintaining a relative flatness are described, for example, in Wiener, U.S. Pat. No. 5,256,468, which describes a type of organization of the fiber optic groups or cables, in which they are held in approximately parallel position and secured by secondary fibers to form a woven mat. By choosing the conditions of weaving and appropriate parameters for materials, the optical fibers can be arranged in a highly parallel and highly planar arrangement, which still permits flexibility of the overall structure without damage to the optical fibers. The fiber matrix may include an elastomeric or resilient coating or support to give the entire structure more stability and protection, as well as to preserve the structural integrity of the optic fibers. The coating and innovative weaving technique enable greater bending with minimal attenuation.
The design of such a woven mat can be modified in a variety of ways. One skilled in the art will understand what choices of material thickness, flexibility, dimension, spacing, and number of optical fibers, and such are appropriate to design an optical matrix with a variety of desirable properties.
In addition to such applications, various fiber optic devices have been used to measure forces, for example, vibration. See, e.g., Tsai, U.S. Pat. No. 7,110,626.
One prior type of fiber optic sensing systems is based on wavelength variations and phase shifts as a function of strain for measuring pressure, weights, or other forces. These systems generally utilize a system of Bragg gratings, and require expensive measuring systems such as interferometers. The costs of such systems are prohibitive in consumer based products such as automobiles. Consequently, many other techniques have been explored in automobiles in regard to sensing the weight and/or position of passengers for appropriate airbag deployment. However, prior to the present invention optical fiber has not been so used.
Many of the solutions presently considered state of the art are very complex, and a more simple and straight forward solution would be useful. What is desired is a simple, robust system for determining both the weight and position of an automobile seat occupant.